Hi, I am trying to enlarge the arrows representing the introns in the GeneRegionTrack

#if it accepts cex like input
scheme$GeneRegionTrack$arrowHeadWidth <- 2 

#if accepts font size like input
scheme$GeneRegionTrack$arrowHeadWidth <- 10

sessionInfo( )
R version 4.1.0 (2021-05-18)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 18.04.5 LTS

Matrix products: default
BLAS:   /usr/lib/x86_64-linux-gnu/blas/libblas.so.3.7.1
LAPACK: /usr/lib/x86_64-linux-gnu/lapack/liblapack.so.3.7.1

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=en_US.UTF-8       
 [4] LC_COLLATE=en_US.UTF-8     LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
 [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                  LC_ADDRESS=C              
[10] LC_TELEPHONE=C             LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
 [1] grid      parallel  stats4    stats     graphics  grDevices utils     datasets 
 [9] methods   base     

other attached packages:
 [1] EnsDb.Hsapiens.v92_0.99.12 ensembldb_2.16.4           AnnotationFilter_1.16.0   
 [4] GenomicFeatures_1.44.1     AnnotationDbi_1.54.1       Biobase_2.52.0            
 [7] Gviz_1.36.2                GenomicRanges_1.44.0       GenomeInfoDb_1.28.1       
[10] IRanges_2.26.0             S4Vectors_0.30.0           BiocGenerics_0.38.0       

loaded via a namespace (and not attached):
 [1] ProtGenerics_1.24.0         bitops_1.0-7               
 [3] matrixStats_0.60.0          bit64_4.0.5                
 [5] filelock_1.0.2              RColorBrewer_1.1-2         
 [7] progress_1.2.2              httr_1.4.2                 
 [9] backports_1.2.1             tools_4.1.0                
[11] utf8_1.2.2                  R6_2.5.0                   
[13] rpart_4.1-15                lazyeval_0.2.2             
[15] Hmisc_4.5-0                 DBI_1.1.1                  
[17] colorspace_2.0-2            nnet_7.3-16                
[19] gridExtra_2.3               tidyselect_1.1.1           
[21] prettyunits_1.1.1           bit_4.0.4                  
[23] curl_4.3.2                  compiler_4.1.0             
[25] htmlTable_2.2.1             xml2_1.3.2                 
[27] DelayedArray_0.18.0         rtracklayer_1.52.1         
[29] checkmate_2.0.0             scales_1.1.1               
[31] rappdirs_0.3.3              stringr_1.4.0              
[33] digest_0.6.27               Rsamtools_2.8.0            
[35] foreign_0.8-81              XVector_0.32.0             
[37] dichromat_2.0-0             htmltools_0.5.1.1          
[39] base64enc_0.1-3             jpeg_0.1-9                 
[41] pkgconfig_2.0.3             MatrixGenerics_1.4.2       
[43] dbplyr_2.1.1                fastmap_1.1.0              
[45] BSgenome_1.60.0             htmlwidgets_1.5.3          
[47] rlang_0.4.11                rstudioapi_0.13            
[49] RSQLite_2.2.7               BiocIO_1.2.0               
[51] generics_0.1.0              BiocParallel_1.26.1        
[53] dplyr_1.0.7                 VariantAnnotation_1.38.0   
[55] RCurl_1.98-1.4              magrittr_2.0.1             
[57] GenomeInfoDbData_1.2.6      Formula_1.2-4              
[59] Matrix_1.3-4                Rcpp_1.0.7                 
[61] munsell_0.5.0               fansi_0.5.0                
[63] lifecycle_1.0.0             stringi_1.7.3              
[65] yaml_2.2.1                  SummarizedExperiment_1.22.0
[67] zlibbioc_1.38.0             BiocFileCache_2.0.0        
[69] blob_1.2.2                  crayon_1.4.1               
[71] lattice_0.20-44             Biostrings_2.60.2          
[73] splines_4.1.0               hms_1.1.0                  
[75] KEGGREST_1.32.0             knitr_1.33                 
[77] pillar_1.6.2                rjson_0.2.20               
[79] biomaRt_2.48.3              XML_3.99-0.7               
[81] glue_1.4.2                  biovizBase_1.40.0          
[83] latticeExtra_0.6-29         data.table_1.14.0          
[85] png_0.1-7                   vctrs_0.3.8                
[87] gtable_0.3.0                purrr_0.3.4                
[89] assertthat_0.2.1            cachem_1.0.5               
[91] ggplot2_3.3.5               xfun_0.25                  
[93] restfulr_0.0.13             survival_3.2-11            
[95] tibble_3.1.3                GenomicAlignments_1.28.0   
[97] memoise_2.0.0               cluster_2.1.2              
[99] ellipsis_0.3.2