There is a difference between bets being PLACED outside of the odds range and bets being MATCHED outside of the odds range.

Placed outside the odds range
There are a couple of reasons why bets may be placed outside of the odds range specified on the Criteria tab:

1. You have told TheBetEngine to check using live trackside odds (Live odds for checks is ticked on the Criteria tab). In this case, TheBetEngine will use the trackside odds for the checks but any bets will be placed at the Betfair odds. As Betfair odds tend to be higher, you can gets bets placed outside of the specified range.

In effect, you are saying "place a bet on Betfair if the live trackside odds fall within my specified range"

Or

2. You have ticked "Win odds for Place" or "Place odds for win" or "BSP for checks" (Criteria tab). In this case, you have told TheBetEngine to use a different set of odds for the odds check than the odds at which you will be betting (you will always be betting at current market odds).

For example - if you have "BSP for checks" ticked then, in effect, you are saying "place a bet on Betfair using the current market odds provided the projected BSP odds fall within my specified odds range"

Or

3. You are placing bets using the 2nd or 3rd best odds. By default, TBE will check the specified odds range against the current best odds, so it is possible that the odds range passes the checks then the bets are placed at lower (or higher) odds. You can alter this behaviour by ticking Allow 2nd/3rd best checks in Settings/General

One way to always set the minimum odds (for a back bet) or the maximum odds (for a lay bet) regardless of what odds you have chosen to use for checking purposes, is to set Use Odds (on the Bet tab) to EXACT and enter the required odds into the accompanying text field.

Matched outside the odds range
On Betfair, it is not possible to:

1. Limit the maximum odds at which Betfair will match a back bet

Or

2. Limit the minimum odds at which Betfair will match a lay bet

This is because Betfair will always match at the best odds available at the time your bet is processed.

For example:
You are backing with an odds range of 1.01 to 2.50, and you request a bet of £5.00 at odds of 2.50. If money becomes available at odds of 2.60 before your bet is processed by Betfair, then you will be matched at odds of 2.60

Note:

If you are placing back bets and have maximised the chances of matching in Settings/Betting, then all back bets are fired in at odds of 1.01, leaving Betfair to match them at the best odds available at the time; these odds could fall outside of your specified range.