Nested Loop vs Hash Join based on predicate?

I have the following queries:

EXPLAIN (ANALYZE, VERBOSE, COSTS, BUFFERS, TIMING)
select […]
from f_calc_service a11,
d_patient_type a12
where a11.d_patient_pop_id in (336)
and a11.d_patient_type_id = a12.id
and a12.short_name = 'I'
group by a11.d_rate_schedule_id,
a11.d_payer_id,
a11.d_patient_pop_id,
a11.d_patient_type_id
;

And

EXPLAIN (ANALYZE, VERBOSE, COSTS, BUFFERS, TIMING)
select […]
from f_calc_service a11,
d_patient_type a12
where a11.d_patient_pop_id in (336)
and a11.d_patient_type_id = a12.id
and a12.short_name = 'O'
group by a11.d_rate_schedule_id,
a11.d_payer_id,
a11.d_patient_pop_id,
a11.d_patient_type_id
;

Making this one change from short_name = ‘I’ to short_name = ‘O’ changes the query execution from 200k ms to 280ms. The first one chooses a Nested Loop, the second chooses a hash join. How do I get them both to choose the same? There are no values for d_patient_pop_id in (336) and short_name = ‘I’.

Thanks!

Dan