In a closed ideal series path, total resistance is R1 + R2 and both resistors carry I = source voltage / total resistance. Source power is source voltage x I. Each resistor dissipates I x I x its resistance. If voltage and total resistance change by the same factor, current stays equal but source power changes. That is a two-variable design comparison, not a test of changing voltage alone. Use paper only, not a physical build.
Worked example
Design X has 2 V and 50 + 50 = 100 ohms: I = 0.02 A and source power = 0.04 W. Design Y has 6 V and 150 + 150 = 300 ohms: I is still 0.02 A, but source power is 0.12 W. Both voltage and resistance tripled. Equal current does not mean equal power.
Three closed series designs
Each design uses an ideal source and constant ideal resistors. Design A: source 4 V; resistors 100 ohms and 100 ohms. Design B: source 8 V; resistors 200 ohms and 200 ohms. Design C: source 12 V; resistors 300 ohms and 300 ohms.