How to rig two bass drums to a yamaha dd75

Hey yall, I've got a Yamaha DD-75 digital drum kit, and I'm trying to connect two Avatar bass drum pedals to it. The DD-75 has two pedal input jacks: one specifically labeled for the bass drum and one for the hi-hat. Here's my dilemma:

• The bass drum pedal works perfectly when plugged into its designated input. It's super responsive and triggers just as expected.
• However, when I plug the second Avatar pedal into the hi-hat input, it's a completely different story. It barely registers a sound. Sometimes, if I stomp on it really hard, or even just plug it in, it'll trigger a sound, but the sensitivity is nowhere near what I need it to be, nor is it comparable to the bass drum input. Essentially, I want both pedals to have similar sensitivity and response, acting as two separate bass drum triggers for the DD-75. I've dug through the DD-75's manual and tried adjusting the hi-hat pedal's sensitivity settings in the function menu, but I haven't been able to get them to match up. Has anyone encountered this before, or does anyone have any tips or tricks for getting external pedals to work consistently with the DD-75's hi-hat input? Any advice on settings, specific pedal types, or even external adapters would be greatly appreciated! Thanks in advance for your help!