It may not be possible to add liquidity to a pool evenly. This is due to the tick spacing of a pool which is relative to the pool's fee tier.
To add liquidity to the pool with 50/50 values, the provider needs to find two ticks that are spaced evenly on both sides of the current price.
For example, if the current price is 3718.19 then an even +/- 1% range would need prices at 3681.0081 and 3755.3719.
Adding liquidity at these exact ticks will result in an equally distributed amount for the position.
However, due to a pool's tick spacing, these exact ticks may not be available. The nearest ticks will be 3677.5136 and 3751.8006.
For more information on automatic price rounding, see this article.