Consider Rising Voltage into a grounded target in Electric Terrain; the user is grounded and benefits from Electric Terrain, and the user has Rivalry with the same gender as the target.
If Rising Voltage was a move with custom base power:
Start with 140 BP.
Chain Electric Terrain (5325) -> Rivalry (5120): 6656
Apply chained modifier - pokeRound(140 * 6656 / 4096) = pokeRound(227.5) = 227 BP
If Rising Voltage was an 8192 base power modifier:
Start with 70 BP.
Chain Rising Voltage (8192) -> Electric Terrain (5325) -> Rivalry (5120): 13313
Apply chained modifier - pokeRound(70 * 13313 / 4096) = pokeRound(227.51708984375) = 228 BP
Take attacker Pincurchin, level 100, 309 Special Attack, into defender Chansey with 246 Special Defense.
Damage rolls with 227 BP:
306, 310, 313, 318, 321, 324, 328, 331, 336, 339, 342, 346, 349, 354, 357, 361
Damage rolls with 228 BP:
307, 312, 315, 318, 322, 325, 330, 333, 337, 340, 343, 348, 351, 355, 358, 363
Actual rolls on cartridge: 306, 313, 318, 328, 336, 339, 342, 357
Conclusion: Rising Voltage was using 227 BP, only possible as a move with custom base power.