Trimming a TH design

[Xevuhtess7]

I would like to build the tapped horn design in this thread: https://www.diyaudio.com/forums/subwoofers/170771-single-sheet-th-challenge.html

However I would like to trim the width from 22" to 21" so it can lay flat in my truck and still close the bed cover. What is an acceptable way to make this adjustment? Should I scale all dimensions down by the same ratio or is it OK to reduce the width only?

Thanks in advance!

 

[weltersys]

OK to reduce the width by 1", which will not change the horn path length, so response should be little different than the original.