The opening statement of the section General Description (opening statements are always a tricky moment) says “In standard English, the phonetic realization of the dental fricative phonemes shows less variation than for many other English consonants”. Leaving aside the grammar of this sentence, it makes a practically unverifiable claim – there is no scientific method that I know of for comparing how much variability there is in the realizations of a given consonant phoneme in comparison with those of other phonemes. In WP, if you make a sweeping claim like this, you are supposed to give a reference for it.
The article continues “Both [/θ/ and /ð/] are pronounced either interdentally, with the blade of the tongue resting against the lower part of the back of the upper teeth and the tip protruding slightly or alternatively with the tip of the tongue against the back of the upper teeth. The interdental position might also be described as "apico-" or "lamino-dental". This section has strong echoes of the discussion of /θ/ and /ð/ by Ladefoged and Maddieson in Sounds of the World’s Languages (pp 143-4), but seems to have misunderstood what they wrote. They (L&M) say that /θ/ and /ð/ may be articulated either with the tip of the tongue behind the upper front teeth or with the tongue-tip protruded between the upper and lower front teeth. They say that the latter (interdental) articulation must be laminal, whereas the articulation with the tongue touching the upper front teeth (dental) may be apical or laminal. (See their illustration below)