Pretty sure any splitter will cut the the signal in half. Weboost sells their own splitter for their at-home systems Splitter -3 dB 2 Way (N-Female) | weBoost
and on the link above there’s this text.
This Wilson Electronics 2-way splitter allows you to drive two interior antennas from a single amplifier. Because you are splitting the signal each antenna will receive approximately 1/2 of the signal …
I’m currently installing a weboost overland, and I plan on using these cable clips https://a.co/d/6sQnb5l so it’s easy to move the internal antenna cord. If/when the clip adhesive fails, I just beef them up with 3m vhb tape. Beyond cleaning with alcohol first, I find using a heat gun on low helps get good adhesion when the temperature is <70F. Helps make sure the alcohol is gone too if I’m being impatient.