Yes it is sometimes annoying that Exchanges often create contract definitions which suit the convenience of their biggest customers (commercial traders) quite well, but make life difficult for small speculators who use one-size-fits-all trading software. The interest rate products on SFE (that you mention) are one example, the forward contracts on LME are another. My personal favorite example of The Ugly Contract Specification is ICE Natural Gas
(link). Just
try to figure out how to tell Blox or AmiBroker or Mechanica or WealthLab or PowerST or (God Forbid) Tradestation, the Variable Parcel Size algorithm that makes BigPointValue fluctuate up and down. Just try.
One ugly and inelegant "solution" that kinda half-ass works, is Incredible Diversification. If the Aussie 10-Year Bond "YTC" is just 2% of your portfolio (i.e. if you're trading >50 markets), then inaccuracies in its BigPointValue are going to have a very small effect on your total account equity. Your calculated open trade profit for positions in YTC will be inaccurate, so your total account equity will be inaccurate, so your position size for new entries will be inaccurate. But since YTC is a very small part of your total trading, the inaccuracies will be small and you may deem them "acceptable".
A simplified example: say you're trading 50 markets and risking 1% of equity on each trade. Say the BPV of the Aussie interest rate contract "YTC" fluctuates by (let's overestimate it:) 20%. Say you've got a really great trade underway in YTC with a huge 10R profit. How big is the error in open trade equity? (10R profit, times 1% risk) means the open trade equity of this YTC trade, is 10% of total account equity. Thanks to BPV inaccuracy, you're off by 20%. 20% of 10% is 2%. So your calculated total account equity in dollars, is wrong by 2%. Position-sizes are being calculated using a total account equity that is off by 2%, so those position sizes are "wrong" by 2%. Can you live with this?
By the way, let me remind you that inaccuracies in BPV can only affect the
magnitude of the open trade equity, they can't affect the
sign. In other words, BPV inaccuracy can't turn a profit into a loss or a loss into a profit.