Call the guy back at Hobbytown USA and tell him he doesn't know what he's talking about.

I've run glow engines in -20 degrees Faihrenheit. I'd be out of flying 1/2 a year if I didn't run them in under 40.

It sounds like you have other issues to sort out before thinking about a pump, or a midrange adjustment. The fuel tank can be lowered...it will just require additional effort. Or, the engine mount can be moved up or down. The options are limitless.

Uniflow, and electric starters are just two of those options. I've never seen an avistar with a uniflow set-up, and I haven't used an electric starter in a long time.

Have you taken the carb apart? Is it clean? I'd check stuff along these lines before I started to lower a tank, or add a pump, etc.