@jonathan-jones If you use "Take Available", the horse has to trade within that range. It's like looking at the market and going "oh ok, this one's in my acceptable range, I'm going to open a trade at that price. E.g. if your range is 4.0 - 7.0 and you spot a selection at 5.0, you open a trade at 5.0. If you set your range to 4.0-4.0, you're saying the horse has to trade at exactly 4.0, no higher or lower.
"Offer Price" means queuing your bet up at a specific price. If you're backing at 4.0 and a horse trades at 4.0 or lower, you'll see an entry bet at 4.0, and vice versa for lays. The price "matched" is always the price you specify, as if your bet was sat there waiting, i.e. if the price goes through your specified price and trades at 5.0 > 4.6 > 4.2 > 3.8, you'd be matched at 4.0, not 3.8.
I think the latter is what you're looking for in this case. In fact, I think in most cases where people enter the same number for the upper and lower price in the "Take Available" range, they're probably actually looking for "Offer Price". I might put a warning in the software to account for that.