You're probably operating under a misconception. Research so far supports the proposition that testosterone esters, e.g. testosterone cypionate, are essentially inert until they reach the bloodstream. Only there do they make contact with enzymes that cleave the testosterone from the ester to make it bioavailable. The implication is that you do not have localized aromatization at injection sites. Though speculative, an alternative explanation is that variations in the rate of testosterone absorption affect the overall rate of aromatization. In particular, there are claims that using testosterone propionate daily leads to less aromatization than using a longer ester such as cypionate. The former results in wide excursions in serum testosterone, while the latter keeps levels relatively steady.
Topical testosterone is a different animal. In this case pure testosterone can interact with the enzymes in the skin, which include aromatase and 5α-reductase. At a given dose rate it's possible to produce more estradiol and DHT with this modality when compared to injections of testosterone esters. Anecdotally it is suggested that estrogenic activity is typically reduced in comparison to injections. The possible mechanisms include greater efficiency of DHT formation and/or the anti-estrogenic effects of DHT itself (aromatase inhibition, estrogen receptor interference).
In conclusion, you may find that using a testosterone gel helps, but if you attain decent absorption then you are likely to see supraphysiological levels of DHT. Personally I'm leery of being out-of-range, but many will dismiss such concerns — because blatant harm has not yet been demonstrated. Alternatively, you might experiment with daily subcutaneous injections of testosterone propionate, or a blend of testosterone propionate and testosterone cypionate.
