The answer to this is very short: no. You have no influence on the size of the test group. This is determined by the system for you. Don't worry, there is a whole calculation behind it. To be precise: your test groups must be large enough for a 95% reliable test. Most statisticians and mathematicians work with this reliability figure.
Since you have no influence at all on which profile variant A and which profile variant B goes to, the A/B test is more valid because our system objectively determines the target group, where you might do this subjectively.
Through the individual reports of variant A and B you can see which profile received which variant.