I know the PST is 16x20, but one more pair of mains is only about a foot longer. I ended up with 17.5" which should leave about 6" on each side. Barely enough to be able to tie a knot, but you will need to use a bridge to pull the last main.
FWIW, I used a half set of VS Touch 16 at 51lbs, pre-stretched on the mains. I did not measure the half set, I just cut a full set in half.
Machines: Gamma 6004 2-point w/ Wise 2086 & Babolat Sensor Dual