As I just learned
from my first AG batch, 144-150 is a good range for the beta amylase but too low for the alpha amylase to work. If you have some mash time in the beta range, you should have some time in the alpha range as well, 150-158. 150-152 would've been ideal to hold the entire 60 min, but if you already had half the time lower than that I would say hold a temp more in the alpha range for the other half. Palmer's How To Brew is a great resource too: http://howtobrew.com/section3/chapter14-5.html
Was the wheat malt unmodified or partially modified? If so, it would require a protein rest around 120-122 before the main mash. That could be another source of low efficiency.