So it looks like the GT911 can have configurable sensitivity either by adjusting the sensitivity threshold or adjusting the gain.

I tried both, however they mainly seem to make it not work

I edited Touch_GT911.cpp:

constexpr uint16_t REG_CONFIG_START = 0x8047;
constexpr size_t CONFIG_LEN = 0x80FF - REG_CONFIG_START;
constexpr size_t TOUCH_SENS_OFF = 0x8053 - REG_CONFIG_START;
constexpr size_t RELEASE_SENS_OFF = 0x8054 - REG_CONFIG_START;
constexpr size_t DAC_GAIN_OFF = 0x806B - REG_CONFIG_START;
constexpr size_t PGA_GAIN_OFF = 0x806C - REG_CONFIG_START;

std::array<uint8_t, 2 + CONFIG_LEN + 2> datas;

// get config
datas[0] = 0x80;
datas[1] = 0x47;
_writeReadBytes(datas.data(), 2, datas.data() + 2, CONFIG_LEN);

// try to change settings - none of these seem to work
datas[2 + TOUCH_SENS_OFF] -= 5;
datas[2 + RELEASE_SENS_OFF] -= 5;
datas[2 + DAC_GAIN_OFF] = 0x00;

// put config
datas[2 + CONFIG_LEN] = 1 + (~std::accumulate(datas.begin() + 2, datas.end() - 2, 0));
datas[2 + CONFIG_LEN + 1] = 0x01;
_writeBytes(datas.data(), datas.size());