For some markets the prices displayed on Betfair may appear to be different to those seen in Bet Angel. This is because Betfair tries to match bets in different ways where possible.
See here for a statement from Betfair.
Bet Angel can compensate for this by switching to the Virtual Bet Display option in the settings area. This forces Bet Angel to use the same cross matching rules that Betfair use when they display available prices on their website.