low zinc may cause a underdevelopement of male organs and function, delayed puberty etc.
I dont know if hypo T affects size directly but it definitely affects its function. Loss of sex drive is one of the many symptoms of hypo T.
I will recommend you to take selenium as taking only Iodine can actually worsen your hypo T. Just dont go overboard with it. Selenium also works well with zinc.
"Selenium, on the other hand, performs many functions. At the beginning of the 1990s it was discovered that the deiodinase enzymes which convert T4 (thyroxin, the thyroid prohormone) into T3 (triiodothyronine, the cellularly active hormone) and also convert T3 into T2, thereby degrading it, are selenium enzymes (formed with the amino acid cysteine). This discovery has led to a lot of research studies on the effects of selenium, iodine, and their interactions" http://www.greenwillowtree.com/Page.bok?file=selenium.iodine.html
Another mineral for you is boron;
"Boron also increases male sex hormone levels. The role of boron supplementation on sex hormone status is not completely understood. It is possible that boron may increase free testosterone levels by contributing to the release of the hormone from sex hormone binding protein (SHBP). SHBP is the protein carrier (acting as a taxi-cab) that shuttles sex hormones through the blood. As men age, SHBP finds it more difficult to release testosterone, keeping it bound and inactive. Boron may increase testosterone, raising levels as much as 50%" http://ezinearticles.com/?Boron-and-Prostate-Health&id=1429932