O/A welding question: tip size

I'm having a welding problem. I'm using an OxyAcy rig. I'm
running 2 psi for each gas thru a .025 diameter tip. I find that in
order to weld join two pieces of .035 tubing with this tip, I must
adjust the flame until it's no larger than 3/16" long. Otherwise
I'm heating up too much of an area and burning away the outer sleeve
(in the case of a splice using an inner sleeve). A flame that small is
very difficult to adjust.

I'm puzzled because the charts I'm looking at show a tip of this
size is appropriate for this size work.

Can you suggest what might be my problem? - Regards, Mike