Good timing, just tore my machine apart yesterday to install my longer rails and have to modify my wiring to reach now.
Thinking I may have to give series a try since I have to re-wire it all anyway….
One thing I found when I switched my printer to DRV’s and 32nd stepping is that apparently some RAMPS boards have traces under the step selection headers so it doesn’t matter what your jumper settings are it’s always as if you have them all installed. Not sure if you’ve checked that on the RAMPS you provide or not but might explain why you didn’t see a difference between 16 and 32 – if those boards have the hidden traces you may not have actually been changing to 16. Just something to check.