Exposure Calculation

I hope someone can tell me what I might be missing here.

I am a market maker/trader for each way exchange markets. I am finding the my exposures, as calculated by Betfair, are way higher than they should be. That in itself is bad enough but I can't make any sense of how they are being calculated by Betfair.

Looking at today's Cheltenham card, the worst possible 1-2-3 or 1-2-3-4 results (for me) would result in a loss of about £3200 (as it stands) but my exposure according to Betfair is nearly 3 times that.

This is not uncommon, it happens all the time, but with higher turnover on a day like today the figures are obviously magnified. At one point, I was getting bet rejected due to account balance being exceeded and I even briefly saw an available funds of minus £400 or so.

Can anyone help shed any light on this? Thanks in advance.