works very well on 4x4.

def imagetransformer_b12l_4h_b256_uncond_dr03_rel_tpu():
  """works very well on 4x4."""
  hparams = imagetransformer_b12l_4h_b256_uncond_dr03_tpu()
  hparams.shared_rel = True
  hparams.dec_attention_type = cia.AttentionType.RELATIVE_LOCAL_1D
  return hparams