Sri can indeed be placed in front of Shiva.
“श्री शिवाय नमस्तुभ्यं" is a very sacred mantra mentioned in Shiva Purana.
It is a misconception that Sri is not placed in front of Bhagwan Shiva. So some people say that Sri is not placed in front of Shiva because Sri is a name of Maa Lakshmi, so it is to be placed only in front of Bhagwan Vishnu or his avatars. Firstly this logic is wrong because the sacred texts do mention that Naam Apradh (differentiating between the names of God) is not to be done. Shiva is Narayan, Bhavani is Lakshmi and it is vice versa also because Devi Purana mentions Shiva as Radha and Parvati as Krishna, so it is not even about male and female in case of Almighty. One Ultimate Power performs different roles, but the eternal truth is one. So there is no point in making things more complicated.
Secondly, Sri is also the name of Maa Lalita Tripurasundari, which proves that it can very much be placed in front of Mahadev. Sri Vidya is considered as the most auspicious one in Shakti Upasana.
Thirdly, Sri is very much used with Shiva. We have Sri Rudram as a very sacred Vedic hymn.
Moreover, Sri can also be placed in front of a normal person. It is used to address a man with respect, likewise Srimati is used to address woman. If it can be used in front of normal people also, then it is obvious to use it front of any name of God.
So Sri can definitely be placed in front of Mahadeva, it is just that in common language, we address him more as Shiv ji than as Shri Shiva.
श्री शिवाय नमस्तुभ्यं 🙏 जय श्री हरि 🙏