Patrick,
regardless of the tool
You want to keep your back straight and not bent.
Spindle height at the elbo is a starting point.
For Spindle work it may be more comfortable to have the lathe an inch or so lower making it easier to work over the top.
for hollowing it may be more comfortable to have the spindle higher.
widening your stance and bending you knees only does so much.
If you use a tool up under your arm you'll be able work more comfortably with a higher lathe.
spindle height like most decisions in woodturning has trade offs.
raising you lathe 6" would may make it difficult to turn spindles and finials and easier to hollow.
One reason I use a trapped hollowing bar is that I can work standing up.
Happy turning,
Al
