Which Bontragers do you have? The bars have different shapes and therefore have different forearm clearances.
Keep in mind that different bars have different reach and drop so changing a bar may require a stem length or angle change or both.
The forearm thing is a normal problem. In the old days (until this year) I used "crit bend" bars to clear the top bend of the bar. Now I use a compact style bar, in my case an FSA Wing/compact bar.
In terms of fit the compact bar is 3 cm shorter and 3 cm more shallow than my old "medium drop back in the day" crit bend bars. This required me to get a stem that made up those dimensions. Due to the old 12 cm stem length I only got back 2.5 cm reach but had to get the 3 cm more drop to position the drops in virtuality the same place as before. This required a custom stem.
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