Finally got my multiband vertical project working across 40m through 10m using quarter-wave stubs and switching relays. Running 34 feet of #14 copper wire vertically with sixteen 10-foot elevated radials at 8 feet AGL.

• Ground losses: Measured 2.1 ohms at antenna base with 8-foot copper ground rod
• Radial current distribution: Using RF ammeter shows fairly even current split
• SWR below 1.5:1 on all bands with relay-switched stub tuning

Question: Would going to thirty-two 8-foot radials vs sixteen 10-footers improve efficiency significantly? Space constraints limit me to about 320 feet total radial wire.

More radials always better than longer radials up to a point. Thirty-two shorter radials will definitely improve your ground plane efficiency over sixteen longer ones. The current distribution gets much more uniform.

Just finished a similar analysis for my contest station vertical. Modeling shows diminishing returns after about 24 radials for elevated systems. Your proposed change should give you maybe 0.5dB improvement - worth doing if you have the wire and time.

Have you considered using the existing sixteen 10-footers but adding sixteen more at different lengths? Mix of 1/4 wave on different bands can broaden the effective ground plane bandwidth. I use 8, 10, 12, and 16-foot radials on my multiband vertical.