intron retention length detected by short read > long read

Question

[shinyjj]

Hi biostars, I found the median length of intron retention detected by short read is generally longer than long read under the same biological sample. Is this because long read sequencing begins from 3' end, but short read can begin both 5' and 3'?

[LChart]

It could simply be because large introns can generate many short reads, while full-length transcripts will generate 1 long read. In other words, just as old-fashioned shotgun RNA-seq is shows a positive relationship between gene length and count, the same should be true of introns.