That's fair, Hobbes, but that's simply your preference. The tracer rules say that every third round you fit in a clip must be a tracer, and that this is an exception to the normal rules of multiple rounds in a clip. I personally think you're overcomplicating things a little, and unnecessarily so.
Allow me to demonstrate. Yes, you have to fire at least two rounds; I assumed that the rules talked about firing at least two tracers, not any two generic rounds. In other words, you have to fire at least six rounds (for example, two regular rounds, one tracer, two regular rounds, one tracer) to gain the benefits of the tracer rounds.
As for remaining rounds in a clip that isn't a multiple of six, it should be as simple as "you don't get the benefit of tracers". In my example I'm using an AK-97 with a Rating 2 extended clip; this means that I've got a clip capacity of 76, but the closest multiple of 6 is 72. So the last four rounds will be regular rounds x2, tracer, regular round x1. I don't gain the benefit of tracers when firing rounds 73 through 76, and I could even choose not to load the last four rounds in the clip; I was personally just going to skip them altogether to avoid confusion.
I'd say specific rule trumps general; if you'd like to house rule how tracers work then that's your prerogative, of course, but respectfully, that's not what's being discussed here. My final thoughts on your application is that real life tracers are a little more complicated than "a dab of phosphorous on the bullet", but that is neither here nor there given what the Shadowrun rules for tracer rounds are.
I am curious to see how previous editions handled this type of ammunition, so I'll go back and check that now just for my own sake.