can't convert opennmt.py model with alibi or rotary embeddings to ctranslate2

I get this error when max_relative_positions: -1 or max_relative_positions: -2

Traceback (most recent call last):
  File "/opt/conda/bin/onmt_release_model", line 33, in <module>
    sys.exit(load_entry_point('OpenNMT-py==3.2.0', 'console_scripts', 'onmt_release_model')())
  File "/opt/conda/lib/python3.10/site-packages/OpenNMT_py-3.2.0-py3.10.egg/onmt/bin/release_model.py", line 35, in main
    converter.convert(opt.output, force=True, quantization=opt.quantization)
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/converter.py", line 89, in convert
    model_spec = self._load()
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/opennmt_py.py", line 189, in _load
    return _get_model_spec_seq2seq(
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/opennmt_py.py", line 89, in _get_model_spec_seq2seq
    set_transformer_spec(model_spec, variables)
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/opennmt_py.py", line 199, in set_transformer_spec
    set_transformer_encoder(spec.encoder, variables)
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/opennmt_py.py", line 204, in set_transformer_encoder
    set_input_layers(spec, variables, "encoder")
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/opennmt_py.py", line 230, in set_input_layers
    set_position_encodings(
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/opennmt_py.py", line 330, in set_position_encodings
    spec.encodings = _get_variable(variables, "%s.pe" % scope).squeeze()
  File "/opt/conda/lib/python3.10/site-packages/ctranslate2/converters/opennmt_py.py", line 334, in _get_variable
    return variables[name].numpy()
KeyError: 'encoder.embeddings.make_embedding.pe.pe'

Start by reproducing the conversion with OpenNMT-py models using max_relative_positions -1 and -2. Trace the path through ctranslate2/converters/opennmt_py.py, especially set_position_encodings and _get_variable, and compare the variables available for these models. Done means both model types convert without the reported KeyError.