saddle fitting questions..too tight on withers

Hi Everyone, Im a relatively new horse owner. I have a colliegate english saddle that I bought used. Ive been using it for months on my horse bc I thought it fit. He does have high withers. He does need to gain muscle in that area. Yesterday my new trainer saw me on him for the first time and said the pommel is too low and that is doesnt fit him. While in the saddle I can only fit one finger in pommel area if that. I asked if it was too far forward but she didnt think so.
I can measure it if you can tell me how to measure a tree of a saddle..(I'll try to find it online) I can take some pics if that helps. To me the pommel looks low on his withers.. And its only rubbed the one time.. (Ive ridden alot) I changed to a thicker pad.. can I get a pad with the withers cut out.. would that help? or does he need a totally differant saddle?
any Info is much appreciated.. pics will be tomorrow after I go to the barn.. thanks,
Melissa

Hi Melissa,  I can appreciate saddle fitting.  We started riding over 30 years ago and had saddle fit problems until we found flex panel saddles. Our customers number in the thousands and love they fit for them and their horses. View our saddles at http://www.asaddle4u.com and see what we offer.

Thanks, Jill