If you check the schematic, the “power path” from battery or USB is the same.
I’m not sure, what you exactly do. Simplified, GPS is used in two modes, “classic” and “assisted”. For “classic”, the GPS receiver starts with receiving “broad-banded”, which isn’t that sensitive. Therefore you need “free sight to the sky”. Once the receiver detect the first signals, it switches to “smaller-banded” mode, which is much more sensitive and may work with less “free sight to the sky”, at least for something about 3h. In the “assisted” mode, the data received in the “broad-banded” phase are exchanged via the cellular protocol and with that, GPS is able to start “smaller-banded”.
That results in:
“classic” requires “initial free sky” and if the device is connected indoor with USB, that doesn’t work
“assisted” doesn’t required that “initial free sky” and may therefore work in less good conditions.